1. Field of the Invention
The present invention relates to a scanning unit for a position measuring instrument for optical scanning of a measuring graduation.
2. Discussion of Related Art
A scanning unit of this kind includes a light source for transmitting light in the direction of the measuring graduation, which is provided with an optically scannable track; a detector, for receiving the light modified, for instance reflected, by the measuring graduation; and a lens array, disposed upstream of the detector and having a plurality of optical lenses, for generating a defined image of a region of the measuring graduation, scanned by the light, on the detector.
Such a scanning unit can be intended for scanning a measuring graduation that has a code track by the incident light process or transmitted light process. In the first case, the light emitted by the light source in the direction of the measuring graduation is modified and reflected by the measuring graduation; in the second case, the light emitted by the light source passes through the (transparent) measuring graduation and is modified in the process.
From European Patent Disclosure EP 1 099 936 A1, a position measuring instrument is known in which a measuring graduation can be scanned by a light source and a detector in the form of a CCD array. Between the measuring graduation provided on a measuring graduation and the detector, a plurality of lenses disposed in one plane side by side are provided, by way of which the measuring graduation disposed on the measuring graduation is projected onto the detector.